Tissue carbon dioxide tension: a putative specific indicator of ischemia in porcine latissimus dorsi flaps

Free flap surgical procedures are technically challenging, and anastomosis failure may lead to arterial or venous occlusion and flap necrosis. To improve myocutaneous flap survival rates, more reliable methods to detect ischemia are needed. On the basis of theoretical considerations, carbon dioxide tension, reflecting intracellular acidosis, may be suitable indicators of early ischemia. It was hypothesized that tissue carbon dioxide tension increased rapidly when metabolism became anaerobic and would be correlated with acute venoarterial differences in lactate levels, potassium levels, and acid-base parameters. Because metabolic disturbances have been observed to be less pronounced in flaps with venous occlusion, it was hypothesized that tissue carbon dioxide tension and venoarterial differences in lactate and potassium levels and acid-base parameters would increase less during venous occlusion than during arterial occlusion. In 14 pigs, latissimus dorsi myocutaneous flaps were surgically isolated, exposed to acute ischemia for 150 minutes with complete arterial occlusion (seven subjects) or venous occlusion (seven subjects), and reperfused for 30 minutes. After arterial occlusion, pedicle blood flow decreased immediately to less than 10 percent of baseline flow. Blood flow decreased more slowly after venous occlusion but within 3 minutes reached almost the same low levels as observed during arterial occlusion. Venous oxygen saturation decreased from approximately 70 percent to approximately 20 percent, whereas oxygen uptake was almost arrested. Tissue carbon dioxide tension increased to two times baseline values in both groups (p < 0.01). The venoarterial differences in carbon dioxide tension, pH, base excess, glucose levels, lactate levels, and potassium levels increased significantly (p < 0.01). Tissue carbon dioxide tension measured during the occlusion period were closely correlated with venoarterial differences in pH, base excess, glucose levels, lactate levels, and potassium levels (median r2, 0.67 to 0.92). After termination of arterial or venous occlusion, more pronounced hyperemia was observed in the arterial occlusion group than in the venous occlusion group (p < 0.05). Oxygen uptake (p < 0.05) and venoarterial differences in lactate and potassium levels (p < 0.05) were significantly more pronounced in the arterial occlusion group. In the venous occlusion group, with less pronounced hyperemia, venoarterial differences in acid-base parameters remained significantly different from baseline values before occlusion (p < 0.01). The data indicate that tissue carbon dioxide tension can be used to detect anaerobic metabolism, caused by arterial or venous occlusion, in myocutaneous flaps. The correlations between carbon dioxide tension and venoarterial differences in acid-base parameters were excellent. Because carbon dioxide tension can be measured continuously in real time, such measurements are more likely to represent a clinically useful parameter than are venoarterial differences.